Lab.gruppen PLM 20000Q - Manual (Page 97)

Application Guide
91
PLM Series Operation Manual rev 1.2.3
Figure 10-6 illustrates how moderate noise with extreme SPL can be achieved. SPL is extremely high in
this example as maximum headroom is available at the input and within the processing stage. This makes it
possible to increase the average SPL by utilizing internal compression capabilities.
▸ Input Clip: 0 dBFS
▸ Amp Gain: 35 dB
▸ SNR: 114.2 dB
▸ Absolute Noise Floor: -71.3 dBu
-140.0
-120.0
-100.0
-80.0
-60.0
-40.0
-20.0
0.0
20.0
40.0
60.0
Analog AES Input Input Mixer Module In Module Out Amp Attenuation Analog Ref Amp Gain ISVPL Output
dB
/d
Bu
Clip
Nominal
Noise
Figure 10-6: Analog Input: Moderate Noise with Very High Output (Very High SPL)
10.5 Speaker Configurations
Connecting two speakers in parallel to a PLM power output presents a load to the amplifier which is half the
impedance of that presented by one speaker. Therefore, the current that two speakers will attempt to draw
from the output stage is double that for one speaker, and this higher current may be sufficient to cause the
Current Peak Limiter to become active. The more speakers connected to an output in parallel, the lower the
impedance and the higher the current draw.
Multiple loudspeakers may be driven by a PLM power output more satisfactorily if a series-parallel wiring
configuration is adopted. Please ensure care is taken to match polarity correctly.
When using series-parallel wiring, the nominal impedance is the same as with one speaker; however, the
principle of power sharing still applies, and it is not possible to get the amplifier section to deliver more than
its rated power.
Nominal loads as low as 2 ohms are supported by the PLM.
However, a 2 ohm nominal load has impedance dips at its
resonances below 2 ohms; in such cases it is likely that the
resulting higher current will cause CPL to activate.